GEOLOGY OF THE NORTHERN ADIRONDACK REGION 397 



sort which usually accompany nephelin syenite igneous bodies, 

 but that such are absent in the immediate region, though occur- 

 ring in Canada to the northward, and to the eastward in New 

 England. It is of course possible that masses of the sort are 

 present in the Champlain region but are as yet uncovered by 

 erosion. It would seem however that these Champlain dikes are 

 on the southeast margin of a considerable region which was 

 alfected by the igneous action, and that evidence regarding their 

 age may be sought in the entire affected area. In the immediate 

 Champlain region no closer determination of their age can be 

 made than that they are younger than the Utica shale, which 

 some of them cut. There would seem to be no question that 

 they are older than the Trias, or are of Paleozoic age, since the 

 igneous rocks of the Trias are of quite different sort, and rocks 

 like these are nowhere found associated with them. The evi- 

 dence given by the exposures on St Helen's island, near Montreal 

 would indicate that these rocks are at least as young as the 

 early Devonic; and the writer has recently come to the belief 

 that a Carboniferous age must be assigned to them, though this 

 is not possible of demonstration at the present time. 



Chemical analyses. No very good and complete analyses of 

 these Champlain eruptives have yet been made, though they 

 closely conform to similar rocks elsewhere. Such as are avail- 

 able are given by Kemp in United States Geological Survey, bul. 

 107. It is however of interest to note their quite striking 

 similarity in composition to the earlier dikes, which preceded 

 them in late Precambric time. The camptonites and monchi- 

 quites are chemically very close to the earlier diabases, and an 

 equally strong resemblance obtains between the bostonites and 

 the syenite porphyries. 



Igneous rocks of the upper Mohawk region. Smyth, G. H. Wil- 

 liams, Darton and Kemp have described very basic rocks, of the 

 perddotite class, about Manheim. Syracuse and Ithaca. 1 These 

 rocks are only remotely connected with the Adirondack region, 

 but completeness would seem to make desirable some considera- 

 tion & Kemp, Am. Jour. Sci. June 1895, p.456-62; Kemp, J. F. Am. 

 Jour. Sci. Nov. 1891, p.410-12 ; Smyth, C. H. Am. Jour. Sci. Ap. 1892, p.322- 



27: Am. Jour. Sci. Aug. 1893, p. 104-7; Geol. Soc. Am. Bul. 9: 257-68; 



Williams. G. H. Am. Jour. Sci. Aug. 1887, p.137-45. 



